Replace the flat module name-to-path mapping with a proper relative import resolver that handles "./" and "../" prefixes relative to the importer's directory. This is a breaking change: existing imports in user code that assume paths are relative to the entrypoint file will now fail. Stack trace output and host API calls now use the resolved module string instead of the short import name. Update all test fixtures to use "./" relative imports and adjust C test files to pass the full resolved module path to wrenGetVariable.
Change bindMethod return type from void to Value to propagate error string when a foreign method's C function pointer is NULL. The call site in runInterpreter now checks for a string error and triggers a runtime error, preventing silent failures on missing foreign bindings.
Add three test cases: foreign method after static declaration, foreign method with a body, and unknown foreign method that expects the new runtime error message.
